How is Heat Transfer Calculated in Ice Melting Problems?

[sdevgon]

1. An amount of ice of mass 80.0g is in a freezer at a temp of -15 degree Celsius. The ice is removed from the freezer, and a total of 19.2KJ of heat is added to the ice. Determine the final temperature of the ice and the mass of ice (if any) which remains after the heat is supplied.



2. Ans is 0 degree Celsius, 30.0g of ice remains



I don't know know how to get that answer. Please help !
Thanks

 

[kuruman]

What do you think happens when you add heat to ice at -15 ^oC? What happens to any solid when you add heat to it?

 

[sdevgon]

adding heat to ice will cause it to melt. But what confused me is 19.2KJ of heat energy. Because i keep taking 19.2KJ of heat energy in consideration when calculating the final temperature.

 

[kuruman]

adding heat to ice will cause it to melt.

Not necessarily. Adding heat to a solid raises its temperature. It will start melting only if it reaches its melting temperature. So the 19.2 kJ of heat energy do two things: (a) first they raise the temperature of the ice from -15 ^oC to 0 ^oC and (b) whatever heat is left over melts as much ice as it can.

But what confused me is 19.2KJ of heat energy. Because i keep taking 19.2KJ of heat energy in consideration when calculating the final temperature.

Why did that confuse you? Of course you should take it in consideration. The final temperature will not rise unless all the ice melts. Evidently, here you don't have enough heat to melt all the ice.